Re: [PATCH] WorkStruct: Implement generic UP cmpxchg() where an arch doesn't support it

[David Howells]

Russell King <rmk+lkml@xxxxxxxxxxxxxxxx> wrote:

> Yes you can.  Well, you can on ARM at least.  Between the load exclusive
> you can do anything you like until you hit the store exclusive.

How come atomic_set() on arm6 is implemented as:

	static inline void atomic_set(atomic_t *v, int i)
	{
		unsigned long tmp;

		__asm__ __volatile__("@ atomic_set\n"
	"1:	ldrex	%0, [%1]\n"
	"	strex	%0, %2, [%1]\n"
	"	teq	%0, #0\n"
	"	bne	1b"
		: "=&r" (tmp)
		: "r" (&v->counter), "r" (i)
		: "cc");
	}

Why LDREX/STREX and not direct assignment?

David
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